U.S. patent number 10,761,141 [Application Number 15/712,389] was granted by the patent office on 2020-09-01 for method and apparatus for estimating battery state.
This patent grant is currently assigned to Samsung Electronics Co., Ltd.. The grantee listed for this patent is SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Jinho Kim, Sungick Kim, Ju Wan Lim, Tae Won Song.
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United States Patent |
10,761,141 |
Song , et al. |
September 1, 2020 |
Method and apparatus for estimating battery state
Abstract
Provided is a method and apparatus for estimating a battery
state. A method of estimating a battery state that includes
determining whether a previous state to a rest state of a battery
is a charging state or a discharging state; selecting a current
profile comprising one or both of a charging pulse and a
discharging pulse based on the previous state of the battery;
stabilizing an open circuit voltage (OCV) of the battery by
applying the current profile to the battery; and measuring the
stabilized OCV.
Inventors: |
Song; Tae Won (Yongin-si,
KR), Lim; Ju Wan (Suwon-si, KR), Kim;
Sungick (Seoul, KR), Kim; Jinho (Yongin-si,
KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRONICS CO., LTD. |
Suwon-si |
N/A |
KR |
|
|
Assignee: |
Samsung Electronics Co., Ltd.
(Suwon-si, KR)
|
Family
ID: |
62108407 |
Appl.
No.: |
15/712,389 |
Filed: |
September 22, 2017 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20180136283 A1 |
May 17, 2018 |
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Foreign Application Priority Data
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Nov 16, 2016 [KR] |
|
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10-2016-0152544 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R
31/3835 (20190101); G01R 31/3828 (20190101); G01R
31/367 (20190101) |
Current International
Class: |
G01R
31/3828 (20190101); G01R 31/3835 (20190101); G01R
31/367 (20190101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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07-098367 |
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Apr 1995 |
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JP |
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2004-362828 |
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Dec 2004 |
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JP |
|
2008-089519 |
|
Apr 2008 |
|
JP |
|
10-2013-0039681 |
|
Apr 2013 |
|
KR |
|
WO 2013/183480 |
|
Dec 2013 |
|
WO |
|
Primary Examiner: Bui; Bryan
Attorney, Agent or Firm: NSIP Law
Claims
What is claimed is:
1. A processor implemented method for an estimation of a battery
state, the method comprising: determining respective operation
states of a battery for plural times, the respective operation
states being determined from among at least one of a rest state, a
charging state, or a discharging state; and performing a
determination of a current state of the battery, including:
determining whether a previous operation state of the battery,
previous to a determined current operation state of the battery
being the rest state, is the charging state or the discharging
state; selecting, based on which of the charging state and the
discharging state the previous operation state is determined to
have been, a current profile in a form that alternately includes at
least one charging pulse and at least one discharging pulse;
performing a stabilizing of an open circuit voltage (OCV) of the
battery by controlling current of the battery according to the
selected current profile; and estimating a battery state of the
battery based on a measuring of a subsequent OCV of the battery
resulting from the performing of the stabilizing.
2. The method of claim 1, wherein a total amount of current of the
charging pulse is equal to a total amount of current of the
discharging pulse.
3. The method of claim 1, wherein the current profile is selected
in a form that starts with a charging pulse in response to the
previous operation state being determined to be the charging
state.
4. The method of claim 1, wherein the current profile is selected
by selecting the current profile in a form that starts with a
discharging pulse in response to the previous operation state being
determined to be the discharging state.
5. The method of claim 1, wherein the performing of the stabilizing
comprises: measuring an instantaneous rate of change of voltage of
the battery; determining whether OCV stabilization of the battery
is achieved based on a determination of whether a magnitude of the
instantaneous rate of change of voltage is less than a threshold;
and performing the estimating of battery state of the battery in
response to the magnitude being determined to be less than the
threshold.
6. The method of claim 1, wherein the battery state of the battery
is a state of charge (SOC) of the battery.
7. The method of claim 6, wherein the estimating of the SOC
comprises: estimating the SOC based on a lookup table corresponding
to the subsequent OCV.
8. The method of claim 1, further comprising: determining whether
the current operation state of the battery is the rest state,
wherein the determining of whether the current operation state of
the battery is the rest state is dependent on one or both of a
charging current and a discharging current being 0 due to passing
of a predetermined time during an operation of the battery, and the
battery being stopped due to passing of the predetermined time and
then operating.
9. The method of claim 1, wherein the determining of whether the
previous operation state is the charging state or the discharging
state is based on consideration of one or both of an instantaneous
SOC rate of change in the current operation state of the battery,
and an accumulation amount of instantaneous rate of changes during
a predetermined time.
10. The method of claim 1, wherein the current profile is in a form
in which at least one rest period is inserted between the
alternately included at least one charging pulse and at least one
discharging pulse.
11. A non-transitory computer-readable medium storing program
instructions that, when executed by a processor, cause the
processor to perform the method of claim 1.
12. An apparatus, the apparatus comprising: a processor configured
to: determine respective operation states of a battery for plural
times, the respective operation states being determined from among
at least one of a rest state, a charging state, or a discharging
state; and perform a determination of a current state of the
battery, wherein, to perform the determination of the current state
of the battery, the processor is further configured to: determine
whether a previous operation state of the battery, previous to a
determined current operation state of the battery being the rest
state, is the charging state or the discharging state; select,
based on which of the charging state and the discharging state the
previous operation state is determined to have been, a current
profile in a form that alternately includes at least one charging
pulse and at least one discharging pulse; perform a stabilization
of an open circuit voltage (OCV) of the battery by controlling
current of the battery according the selected current profile;
measure a subsequent OCV of the battery resulting from the
performed stabilization; and estimate a state of charge (SOC) of
the battery based on the measured subsequent OCV.
13. The apparatus of claim 12, wherein a total amount of current of
the charging pulse is equal to a total amount of current of the
discharging pulse.
14. The apparatus of claim 12, wherein the processor is further
configured to select the current profile in a form that starts with
a charging pulse in response to the previous operation state being
determined to be the charging state.
15. The apparatus of claim 12, wherein the processor is further
configured to select the current profile in a form that starts with
a discharging pulse in response to the previous operation state
being determined to be the discharging state.
16. The apparatus of claim 12, wherein the processor is further
configured to measure an instantaneous rate of change of voltage of
the battery, determine whether OCV stabilization of the battery is
achieved based on whether a magnitude of the instantaneous rate of
change of voltage is less than a threshold, and to perform the
estimation of the SOC in response to the magnitude being determined
less than the threshold.
17. The apparatus of claim 12, further comprising: a memory
configured to store a lookup table corresponding to the subsequent
OCV, wherein the processor is further configured to perform the
estimation of the SOC based on the lookup table.
18. The apparatus of claim 12, wherein the processor is further
configured to determine whether the current operation state of the
battery is the rest state, and the determination of whether the
current operation state of the battery is the rest state is
dependent on one or both of a charging current or a discharging
current being 0 due to passing of a predetermined time during an
operation of the battery, and the battery being stopped due to
passing of the predetermined time and then operating.
19. The apparatus of claim 12, wherein the processor is further
configured to perform the determination of whether the previous
battery rest state is the charging state or the discharging state
based on consideration of one or both of an instantaneous SOC rate
of change and an accumulation amount of instantaneous rate of
changes during a predetermined time.
20. The apparatus of claim 12, wherein the current profile is in a
form in which at least one rest period is inserted between the
alternately included at least one charging pulse and at least one
discharging pulse.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit under 35 USC .sctn. 119(a) of
Korean Patent Application No. 10-2016-0152544 filed on Nov. 16,
2016 in the Korean Intellectual Property Office, the entire
disclosure of which is incorporated herein by reference for all
purposes.
BACKGROUND
1. Field
The following description relates to technology for estimating a
state of a battery.
2. Description of Related Art
A battery is used as a power source, for example, of a mobile
device, an electric vehicle, etc. To stably use the battery during
a relatively long lifespan of the battery, it is very important to
accurately estimate the charging state of the battery. If the
charging state of the battery is inaccurately estimated,
overcharging or over-discharging may occur during charging or
discharging of the battery.
A variety of schemes have been proposed to estimate the charging
state of the battery. A current integration method, for example, an
Ah method or a Coulomb counting method, is a method of estimating
state of charge (SOC) based on a charging/discharging current and
time of the battery, and a resistance measurement method is a
method of estimating SOC based on a relationship between an
internal resistance of the battery and the SOC. The current
integration method and the resistance measurement method may
estimate a charging state of a battery in operation, however, do
not apply an internal electrochemical characteristic of the battery
once the operation of the battery is terminated. A voltage
measurement method estimates SOC based on an open circuit voltage
(OCV) of the battery and thus, may estimate an initial charging
state of the battery that operates again after the operation of the
battery is terminated.
To estimate the charging state of the battery based on the OCV of
the battery, a predetermined amount of time is required to
stabilize an internal state of the battery. Also, an OCV determined
based on the charging of the battery and the discharging of the
battery do deviate at the same SOC. This phenomenon is referred to
as an OCV hysteresis. Due to the OCV hysteresis, an error may occur
in estimating the battery state. Accordingly, there is a need for
technology for further accurately estimating the state of a battery
and reducing the stabilization time of the battery.
SUMMARY
This Summary is provided to introduce a selection of concepts in a
simplified form that are further described below in the Detailed
Description. This Summary is not intended to identify key features
or essential features of the claimed subject matter, nor is it
intended to be used as an aid in determining the scope of the
claimed subject matter.
In one general aspect, a method of estimating a battery state
includes determining whether a previous state of a battery in a
rest state is a charging state or a discharging state, selecting a
current profile including a charging pulse and a discharging pulse
based on the previous state of the battery, stabilizing an open
circuit voltage (OCV) of the battery by applying the current
profile to the battery, and measuring the stabilized OCV.
A total amount of current of the charging pulse may be equal to a
total amount of current of the discharging pulse.
The selecting may include selecting a current profile in a form
that starts with a charging pulse in response to the previous state
of the battery being determined to be the charging state.
The selecting may include selecting a current profile in a form
that starts with a discharging pulse in response to the previous
state of the battery being determined to be the discharging
state.
The stabilizing may include measuring an instantaneous rate of
change of voltage of the battery, and determining whether the OCV
of the battery is stabilized based on whether a magnitude of the
instantaneous rate of change of voltage is less than a
threshold.
The battery state estimation method may further include estimating
a state of charge (SOC) of the battery based on the measured
OCV.
The estimating may include estimating the SOC by referring to a
lookup table corresponding to the stabilized OCV.
The battery state estimation method may further include determining
whether the battery is in the rest state. The rest state may
include at least one of a case in which a charging current or a
discharging current is .alpha. due to passing of a predetermined
time during an operation of the battery and a case in which the
battery is stopped in response to passing of the predetermined time
and then operated.
The determining may include determining whether the previous state
of the battery is the charging state or the discharging state based
on at least one of an instantaneous rate of change of an SOC of the
battery in the rest state and an accumulation amount of
instantaneous rate of changes during a predetermined time.
The current profile may be in a form in which at least one rest
period is inserted between the alternately included charging pulse
and discharging pulse.
In another general aspect, an apparatus for estimating a battery
state includes a processor configured to determine whether a
previous state of a battery in a rest state is a charging state or
a discharging state, to select a current profile in a form that
alternately includes charging pulse and discharging pulse based on
a result of the determining, to stabilize an OCV of the battery by
applying the current profile to the battery, to measure the
stabilized OCV, and to estimate a SOC of the battery based on the
measured OCV.
Other features and aspects will be apparent from the following
detailed description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart illustrating an example of a battery state
estimation method.
FIG. 2A illustrates an example of a process of stabilizing an open
circuit voltage (OCV) based on a current profile.
FIG. 2B illustrates an example of a process of stabilizing a
concentration distribution within a battery based on a current
profile.
FIGS. 3A through 3D illustrate examples of a current profile.
FIG. 4 is a flowchart illustrating an example of a battery state
estimation method.
FIG. 5 illustrates an example of a source of a current profile.
FIG. 6 is a block diagram illustrating an example of a battery
state estimation apparatus.
Throughout the drawings and the detailed description, unless
otherwise described or provided, the same drawing reference
numerals will be understood to refer to the same elements,
features, and structures. The drawings may not be to scale, and the
relative size, proportions, and depiction of elements in the
drawings may be exaggerated for clarity, illustration, and
convenience.
DETAILED DESCRIPTION
The following detailed description is provided to assist the reader
in gaining a comprehensive understanding of the methods,
apparatuses, and/or systems described herein. However, various
changes, modifications, and equivalents of the methods,
apparatuses, and/or systems described herein will be apparent after
an understanding of the disclosure of this application. For
example, the sequences of operations described herein are merely
examples, and are not limited to those set forth herein, but may be
changed as will be apparent after an understanding of the
disclosure of this application, with the exception of operations
necessarily occurring in a certain order. Also, descriptions of
features that are known in the art may be omitted for increased
clarity and conciseness.
The features described herein may be embodied in different forms,
and are not to be construed as being limited to the examples
described herein. Rather, the examples described herein have been
provided merely to illustrate some of the many possible ways of
implementing the methods, apparatuses, and/or systems described
herein that will be apparent after an understanding of the
disclosure of this application.
The following structural or functional descriptions are exemplary
to merely describe the examples, and the scope of the examples is
not limited to the descriptions provided in the present
specification. Various changes and modifications can be made
thereto by those of ordinary skill in the art.
Although terms of "first" or "second" are used to explain various
components, the components are not limited to the terms. These
terms should be used only to distinguish one component from another
component. For example, a "first" component may be referred to as a
"second" component, or similarly, and the "second" component may be
referred to as the "first" component within the scope of the right
according to the concept of the present disclosure.
It will be understood that when a component is referred to as being
"connected to" another component, the component can be directly
connected or coupled to the other component or intervening
components may be present.
As used herein, the singular forms are intended to include the
plural forms as well, unless the context clearly indicates
otherwise. It should be further understood that the terms
"comprises" and/or "comprising," when used in this specification,
specify the presence of stated features, integers, steps,
operations, elements, components or a combination thereof, but do
not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
Unless otherwise defined herein, all terms used herein including
technical or scientific terms have the same meanings as those
generally understood by one of ordinary skill in the art. Terms
defined in dictionaries generally used should be construed to have
meanings matching with contextual meanings in the related art and
are not to be construed as an ideal or excessively formal meaning
unless otherwise defined herein.
Hereinafter, examples will be described in detail with reference to
the accompanying drawings, and like reference numerals in the
drawings refer to like elements throughout.
FIG. 1 illustrates an example of a battery state estimation
method.
Referring to FIG. 1, in operation 101, a battery state estimation
apparatus determines whether a previous state of a battery in a
rest state is a charging state or a discharging state. The battery
may include an electric condenser or a secondary cell configured to
store power by charging. A device that uses the battery may supply
the power from the battery to a load. The load is an entity that
consumes power and the power may be externally supplied. For
example, the load may be an electric heater, a light, or a motor of
an electric vehicle that consume power using a circuit in which
current flows at a specific voltage. Here, the battery of which a
state is to be estimated may include one or more battery packs that
include a plurality of battery modules, one or more battery modules
within the battery pack, a battery module that includes a plurality
of battery cells, one or more battery cells within the battery
module, a representative module that represents a plurality of
battery modules, and a representative cell that represents a
plurality of battery cells. Hereinafter, the battery is understood
to refer to any one or combination of the above examples.
The battery state estimation apparatus estimates the state of the
battery, and may be configured as a software module, a hardware
module, and/or various combinations thereof. For example, the
battery state estimation apparatus may be configured by a battery
management system (BMS). The BMS is a system that manages the
battery, and for example, monitors the state of the battery,
maintains an optimal condition for an operation of the battery,
predicts a replacement timing of the battery, detects a fault of
the battery, generates a control signal or a command signal
associated with the battery, and/or controls the state or the
operation of the battery.
The rest state of the battery includes a state in which the battery
is not being charged or discharged. For example, the rest state
includes a case in which the charging current or the discharging
current is 0 due to passing of a predetermined time during an
operation of the battery, and/or the battery is stopped due to
passing of the predetermined time and then operates.
The previous state of the battery in the rest state indicates the
battery state before the battery enters into the rest state. The
battery state estimation apparatus may determine whether the
battery is being charged or discharged, that is, whether the
battery is in a charging state or in a discharging state before
entering into the rest state. For example, if an electric vehicle
to which the battery is mounted is currently stopped in front of a
stop signal light after driving on the road, the battery state
estimation apparatus determines that the battery is in the rest
state and that the previous state of the battery in the rest state
is the discharging state. If the electric vehicle in which the
battery is mounted is currently stopped after driving on a downhill
road, the battery state estimation apparatus may determine that the
battery is in the rest state and that the previous state of the
battery in the rest state is in the charging state. In the case of
driving on the downhill road, the battery may be charged through
regenerative braking. If the ignition of the electric vehicle of
which battery charging is completed is turned off and then turned
on at a charging station, the battery state estimation apparatus
may determine that the battery is in the rest state and may
determine that the previous state of the battery in the rest state
is the charging state.
The battery state estimation apparatus may determine whether the
previous state of the battery is the charging state or the
discharging state based on an instantaneous rate of change of a
state of charge (SOC) of the battery in the rest state and/or an
accumulation amount of instantaneous rate of changes during a
predetermined time. The SOC is a parameter that indicates the
charging state of the battery. The SOC represents a level of energy
stored in the battery and the amount of SOC may be expressed as 0
to 100% using a percentage (%) unit. For example, 0% denotes a
completely discharged state and 100% denotes a fully charged state.
The representation scheme may be modified and defined based on
design intent or examples. The instantaneous rate of change of SOC
indicates an instantaneous rate of change of SOC over time. Since
the SOC increases or decreases due to charging or discharging, the
battery state estimation apparatus may verify the previous state of
the battery in the rest state based on the instantaneous rate of
change of SOC. For example, the battery state estimation apparatus
determines whether the previous state of the battery is the
charging state or the discharging state by deriving a gradient from
a function of the SOC over time by performing a differential
operation.
Referring again to FIG. 1, after determining whether the previous
state of the battery in a rest state is a charging state or a
discharging state in operation 101, in operation 102, the battery
state estimation apparatus selects a current profile in a form that
alternately includes at least one charging pulse and at least one
discharging pulse based on the result. Here, the current profile
represents a policy for determining a scheme for applying a
charging pulse or a discharging pulse to the battery, and may be
defined as a form that includes at least one charging pulse and at
least one discharging pulse. A charging pulse or a discharging
pulse is a pulse to be applied to the battery of which the state is
to be estimated, and includes a charging current or a discharging
current in a pulse form. In response to applying the charging pulse
to the battery, a charging current flows in the battery. In
response to applying the discharging pulse to the battery, a
discharging current flows out from the battery. A physical
quantity, for example, the shape of the pulse over time, amplitude,
pulse unit, etc., used to define the charging pulse or the
discharging pulse may be variously modified and configured based on
the design intent.
In one example, the current profile is defined in a form that
alternately includes at least one charging pulse and at least one
discharging pulse. Here, the total amount of current of the
charging pulse may be equal to the total amount of current of the
discharging pulse. Although the current profile defined in a form
in which the amount of current of charging pulses and discharging
pulses are different is applied to the battery, it is possible to
prevent overcharging or over-discharging from occurring in the
battery compared to a current state by equalizing a amount of
current between the charging pulses and the discharging pulses.
Also, although the current profile defined in the form in which the
amount of current of charging pulses and discharging pulses are
different may be applied to a battery pack, a battery module, a
battery cell, a representative module, or a representative cell, it
is possible to prevent a charging state between a battery to which
the current profile is applied and a battery to which the current
profile is not applied from varying by equalizing a amount of
current between the charging pulses and the discharging pulses.
If the previous state of the battery is the charging state, the
battery state estimation apparatus selects a current profile in a
form that starts with a charging pulse. In this example, the
current profile is designed to apply charging pulses and
discharging pulses to the battery sequentially in a pattern of
charging pulse->discharging pulse.
If the previous state of the battery is the discharging state, the
battery state estimation apparatus selects a current profile in a
form that starts with a discharging pulse. In this example, the
current profile is designed to apply charging pulses and
discharging pulses to the battery sequentially in a pattern of
discharging pulse->charging pulse. Here, setting the order of
the charging pulse and the discharging pulse is modified based on
the design intent; thus, not limited to the aforementioned
patterns.
In operation 103, the battery state estimation apparatus stabilizes
an open circuit voltage (OCV) of the battery by applying the
current profile to the battery. The OCV refers to the battery
voltage in a state in which an internal circuit is open, and is
measured or estimated as a value to which the battery voltage
converges over time from a state in which a current flowing in the
battery is 0.
FIG. 2A illustrates an example of a process of stabilizing an OCV
based on a current profile.
Referring to an upper graph of FIG. 2A, a battery is being
discharged with a discharging current of the battery constantly
flowing and a discharging current of 0 is applied to the battery at
a certain point in time. Here, a positive current indicates
discharging of the battery and a negative current indicates
charging of the battery. The voltage of the battery decreases in
response to discharging of the battery. The voltage of the battery
converges to a predetermined voltage value from a point in time at
which the discharging current becomes zero and discharging of the
battery is stopped. In one example, the OCV of the battery is
estimated based on a value to which the voltage of the battery
converges.
An OCV stabilization time 204 denotes an amount of time used to
estimate the OCV of the battery. In detail, the OCV stabilization
time 204 denotes an amount of time used to stabilize the voltage of
the battery in a rest state through constant convergence to a level
that allows OCV estimation. In one example, the OCV stabilization
time is about 30 minutes. The amount of time used to estimate the
OCV increases in response to an increase in the OCV stabilization
time. Thus, the OCV stabilization time needs to be reduced.
Referring to a lower graph of FIG. 2A, the battery state estimation
apparatus stabilizes the OCV of the battery by applying a current
profile 201 to the battery in the rest state. Stabilizing the OCV
of the battery means enabling an operation where the voltage of the
battery constantly converges to a predetermined voltage value and
reducing an OCV stabilization time to estimate the OCV of the
battery. The battery state estimation apparatus applies the current
profile 201 that starts with a discharging pulse to the battery
based on the fact that a previous state of the battery in the rest
state is a discharging state. The battery state estimation
apparatus reduces the OCV stabilization time of the battery by
applying the current profile 201 to the battery in the rest
state.
Referring to the lower graph of FIG. 2A, by applying the current
profile 201 to the battery, the OCV of the battery is stabilized
and the OCV stabilization time 201 is reduced compared to the OCV
stabilization time 204 in which the current profile 201 is not
applied. A voltage 207 of the battery over time, when the current
profile 201 is applied to the battery in the rest state, further
quickly converges to the OCV compared to a voltage 206 of the
battery over time when the current profile is not applied to the
battery.
If the difference between a specific voltage and a voltage of the
battery at a specific point in time after the OCV stabilization
time 204 is elapsed is .DELTA.V 205, a difference .DELTA.V 203 of
the battery to which the current profile 201 is applied is less
than the difference .DELTA.V 205 of the battery to which the
current profile 201 is not applied. An OCV of the battery to which
the current profile 201 is applied is greater than the battery to
which the current profile 201 is not applied. Accordingly, the
battery state estimation apparatus reduces OCV estimation errors
based on OCV hysteresis by applying the current profile 201 to the
battery in the rest state. Dissimilar to FIG. 2A, if the previous
state of the battery in the rest state is a charging state, the
difference .DELTA.V 203 of the battery to which the current profile
201 is applied is reduced and .DELTA.V of the battery is estimated
as a relatively small value compared to a case in which the current
profile 201 is not applied.
In one example, the battery state estimation apparatus iteratively
applies a current profile to a battery to stabilize an OCV of the
battery. The battery state estimation apparatus determines whether
the OCV of the battery is stabilized, and iteratively applies the
current profile to the battery based on a determination result.
Here, the current profile to be additionally applied is designed to
be different from the initially applied current profile.
The battery state estimation apparatus measures an instantaneous
rate of change of the battery to determine whether the OCV is
stabilized. Here, the instantaneous rate of change indicates an
instantaneous rate of change of voltage over time. The battery
state estimation apparatus compares a magnitude of the
instantaneous rate of change of voltage to a threshold. If the
magnitude of the instantaneous rate of change of voltage is less
than the threshold, the battery state estimation apparatus
determines that the OCV of the battery is stabilized.
FIG. 2B illustrates an example of a process of stabilizing a
concentration distribution within a battery based on a current
profile.
The battery stores energy using an electrochemical reaction between
ions, for example, positive ions with positive charge present
around particles of a cathode and ions, for example, negative ions
with negative charge present around particles of an anode. In
response to charging or discharging of the battery, the
concentration distribution of positive ions present inside and
around particles of the cathode and the concentration distribution
of negative ions present inside and around particles of the anode
vary. If the battery is in a rest state, the concentration
distribution inside and around particles of the cathode and the
concentration distribution inside and around particles of the anode
may be stabilized. With the stabilization of the concentration
distributions, the OCV of the battery may also be stabilized. The
stabilization of the concentration distributions associated with
the cathode and the anode indicates that the concentration
distribution from the internal center to the surface of particles
of the cathode and the anode becomes constant.
FIG. 2B shows the concentration distribution of positive ions
inside and around particles of the cathode CA and the concentration
distribution of negative ions inside and around particles of the
anode AN. Here, although a particle of the cathode CA and a
particle of the anode AN are illustrated to be in a planar form,
they may be in a form of a three-dimensional (3D) sphere. In the
graphs of FIG. 2B, x axis denotes a radius r and y axis denotes
concentration, for example, lithium (Li) concentration. The battery
state estimation apparatus may apply a current profile, for
example, the current profile 201 of FIG. 2A to the battery in the
rest state. Leftmost graphs show the concentration distributions
inside and around particles before the current profile 201 is
applied. Center graphs show the concentration distributions varying
based on the particle surface by applying the current profile 201
to the battery. Rightmost graphs show the concentration
distributions being gradually stabilized inside and around
particles.
Referring again to FIG. 1, in operation 104, the battery state
estimation apparatus measures the stabilized OCV. Various schemes
for measuring the OCV may be employed and examples are not limited
to a specific scheme.
The battery state estimation apparatus measures the SOC of the
battery based on the measured OCV. In one example, the battery
state charging apparatus estimates the SOC of the battery using a
voltage measurement method. For example, the battery state
estimation apparatus pre-stores a lookup table corresponding to the
stabilized OCV. The battery state estimation apparatus acquires the
lookup table corresponding to the stabilized OCV from a
preconfigured database. The database is configured as a memory
included in the battery state estimation apparatus, or as an
external device of a server connectable to the battery state
estimation apparatus in a wired or wireless manner, or over a
network.
The battery state estimation apparatus uses the lookup table
corresponding to the stabilized OCV. Thus, there is no need to
separately manage a lookup table corresponding to a charging state
and a lookup table corresponding to a discharging state, and it is
possible to reduce an error in estimating the state of the battery,
which occurs due to an OCV hysteresis.
In one example, the battery state estimation apparatus may estimate
SOC of a battery based on a function relationship between the
stabilized OCV and the SOC. Also, the battery state estimation
apparatus may estimate the SOC of the battery by applying the
stabilized OCV to an electric circuit or an electrochemical
model.
FIGS. 3A through 3D illustrate examples of a current profile.
As described above, the current profile is designed to alternately
include at least one charging pulse and at least one discharging
pulse. Referring to FIGS. 3A through 3D, the total amount of
current of the charging pulse the discharging pulse are equal.
Referring to FIG. 3B, in one example, the current profile is
designed in a form in which at least one rest period, for example,
C of FIG. 3B, is inserted between the alternating charging pulse
and discharging pulse.
In FIG. 3C, the duration of the charging pulse is a fraction of the
discharging pulse. FIG. 3D depicts the summation of charging pulse
widths and amplitudes being equal to the summation of the
discharging pulse widths and amplitudes. The relationship between
the charging and discharging pulse widths and amplitudes is
expressed as
.SIGMA.(A.sub.i.times.a.sub.i)=.SIGMA.(B.sub.j.times.b.sub.j).
where A is the charging pulse width, a is the charging amplitude, i
and j are integers, B is the discharging pulse width, and b is the
discharging amplitude.
The current profiles of FIGS. 3A through 3D are provided as
examples only and the battery state estimation apparatus may be
designed so that the current profile includes various combinations
and duty cycles of the charging pulse and the discharging
pulse.
FIG. 4 illustrates an example of a battery state estimation
method.
Referring to FIG. 4, in operation 401, a battery state estimation
apparatus determines whether a battery is in operation. For
example, if an electric vehicle to which the battery is mounted is
driving or temporarily stopped after driving, the battery is
operating.
In operation 402, the battery state estimation apparatus determines
whether a charging current or a discharging current of the battery
in operation is 0. Unless the charging current or the discharging
current of the battery is 0, the battery state estimation apparatus
determines that t.sub.rest is 0 and estimates SOC of the battery in
operation 403. Here, t.sub.rest denotes an amount of time in which
the charging current or the discharging current of the battery is
maintained to be 0. The battery of which t.sub.rest is 0 is not in
the rest state. Thus, the battery state estimation apparatus
estimates the SOC of the battery using at least one of a current
integration method, a resistance measurement method, and an
electrochemical model estimation method, or various combinations
thereof.
If the charging current or the discharging current of the battery
is 0, the battery state estimation apparatus determines whether the
operation of the battery is suspended in operation 404. If the
operation of the battery is suspended, the battery is in the rest
state and the battery state estimation apparatus determines whether
a previous state of the battery in the rest state is a charging
state or a discharging state in operation 407.
If the operation of the battery is not suspended, the battery state
estimation apparatus determines whether t.sub.rest is less than a
threshold in operation 405. If is less than the threshold, the
battery state estimation apparatus adds a predefined time .DELTA.t
to t.sub.rest in operation 406, and determines whether the charging
current or the discharging current of the battery is 0 in operation
402.
If the previous state of the battery is the charging state, the
battery state estimation apparatus alternately applies charging
current and discharging current to the battery in operation 408. As
described above, the battery state estimation apparatus may
alternately apply the charging current and the discharging current
by applying a current profile to the battery. In operation 409, the
battery state estimation apparatus determines whether a magnitude
of an instantaneous rate of change of voltage of the battery to
which the charging current and the discharging current are
alternately applied is less than the threshold. If the magnitude of
the instantaneous rate of change of voltage of the battery is less
than the threshold, the battery state estimation apparatus measures
a stabilized OCV of the battery in operation 412. If the magnitude
of the instantaneous rate of change of voltage of the battery is
greater than or equal to the threshold, the battery state
estimation apparatus alternately applies again the charging current
and the discharging current to the battery in operation 408.
If the previous state of the battery is the discharging state, the
battery state estimation apparatus alternately applies the
discharging current and the charging current to the battery in
operation 410. As described above, the battery state estimation
apparatus may alternately apply the discharging current and the
charging current to the battery by applying the current profile to
the battery. In operation 411, the battery state estimation
apparatus determines whether a magnitude of an instantaneous rate
of change of voltage of the battery to which the discharging
current and the charging current are alternately applied is less
than the threshold. If the magnitude of the instantaneous rate of
change of voltage of the battery is less than the threshold, the
battery state estimation apparatus measures the stabilized OCV of
the battery in operation 412. If the magnitude of the instantaneous
rate of change of voltage of the battery is greater than or equal
to the threshold, the battery state estimation apparatus
alternately applies again the discharging current and the charging
current to the battery in operation 410.
In operation 413, the battery state estimation apparatus measures
the SOC of the battery based on the measured OCV. The
aforementioned examples associated with the SOC estimation may be
applicable.
The example of stabilizing the OCV of the battery in the rest state
in a case in which the battery in operation enters into the rest
state is described with reference to FIG. 4. In a case in which the
battery is stopped due to passing of a predetermined time and then
operates, the battery state estimation apparatus may determine
whether the battery is in the rest state and may stabilize the OCV
of the battery in the rest state. For example, the battery mounted
to the electric vehicle may operate in a battery stop state in
response to turning on ignition of the electric vehicle. In one
example, the battery state estimation apparatus may stabilize the
OCV of the battery in the rest state by applying the aforementioned
examples.
FIG. 5 illustrates an example of a source of a current profile.
Referring to FIG. 5, a source of a current profile applied to a
battery 501 includes an external power source 502 and an internal
power source 503. The source of the current profile indicates an
entity that supplies a charging pulse and a discharging pulse to be
applied to the battery 501 based on the current profile.
In one example, a battery state estimation apparatus alternately
applies at least one charging current and at least one discharging
current to the battery 501 from the external power source 502 that
is a source of the current profile 504. Alternately, charging and
discharging current may be applied through a separate circuit. The
external power source 502 is an independent power source separate
from the battery 501 to which the current profile 504 is applied,
and includes, for example, a charger of a charging station, a
backup battery, and the like.
In one example, the battery state estimation apparatus alternately
applies at least one charging current and at least one discharging
current to the battery 501 from the internal power source 503 that
is a source of the current profile 505. Alternatively, charging and
discharging current may be applied through a separate circuit. The
internal power source 503 includes a battery that supplies power in
association with the battery 501 to which the current profile 505
is applied, and includes, for example, at least one of a battery of
which a load that is a power supply target is the same as that of
the battery 501, a battery module that belongs to the same battery
pack as the battery 501, and a battery cell that belongs to the
same battery module as the battery 501.
Referring to FIG. 5, since the internal power source 503 is the
source of the current profile 505 that is applied to the battery
501, the battery 501 may become a source of the current profile 506
to be applied to the internal power source 503. In one example, the
current profile 505 applied to the battery 501 and the current
profile 506 applied to the internal power source 503 are provided
in a symmetric form based on a time axis. Accordingly, if the
internal power source 503 is used as the source of the current
profile 505 applied to the battery 501, the battery state
estimation apparatus simultaneously stabilizes an OCV of the
battery 501 and an OCV of the internal power source 503, and
constantly maintains charging states or SOC of the battery 501 and
the internal power source 503.
FIG. 6 illustrates an example of a battery state estimation
apparatus.
Referring to FIG. 6, a battery state estimation apparatus 601
includes a processor 602 and a memory 603. The processor 602 may
include at least one of the apparatuses described with FIGS. 1
through 5, or may perform at least one of the methods described
with FIGS. 1 through 5. The memory 603 stores a lookup table
corresponding to a stabilized OCV of a battery or stores a program
in which a battery state estimation method is configured. The
memory 603 may be a volatile memory or a nonvolatile memory.
The processor 602 executes the program and controls the battery
state estimation apparatus 601. A code of the program executed by
the processor 602 may be stored in the memory 603. The battery
state estimation apparatus 601 is connected to an external device,
for example, a PC or a network through an input/output (I/O) device
(not shown) and exchanges data.
Examples of hardware components include controllers, sensors,
generators, drivers, and any other electronic components known to
one of ordinary skill in the art. In one example, the hardware
components are implemented by one or more processors or computers.
A processor or computer is implemented by one or more processing
elements, such as an array of logic gates, a controller and an
arithmetic logic unit, a digital signal processor, a microcomputer,
a programmable logic controller, a field-programmable gate array, a
programmable logic array, a microprocessor, or any other device or
combination of devices known to one of ordinary skill in the art
that is capable of responding to and executing instructions in a
defined manner to achieve a desired result. In one example, a
processor or computer includes, or is connected to, one or more
memories storing instructions or software that are executed by the
processor or computer. Hardware components implemented by a
processor or computer execute instructions or software, such as an
operating system (OS) and one or more software applications that
run on the OS, to perform the operations described herein. The
hardware components also access, manipulate, process, create, and
store data in response to execution of the instructions or
software. For simplicity, the singular term "processor" or
"computer" may be used in the description of the examples described
herein, but in other examples multiple processors or computers are
used, or a processor or computer includes multiple processing
elements, or multiple types of processing elements, or both. In one
example, a hardware component includes multiple processors, and in
another example, a hardware component includes a processor and a
controller. A hardware component has any one or more of different
processing configurations, examples of which include a single
processor, independent processors, parallel processors,
single-instruction single-data (SISD) multiprocessing,
single-instruction multiple-data (SIMD) multiprocessing,
multiple-instruction single-data (MISD) multiprocessing, and
multiple-instruction multiple-data (MIMD) multiprocessing.
Instructions or software to control a processor or computer to
implement the hardware components and perform the methods as
described above are written as computer programs, code segments,
instructions or any combination thereof, for individually or
collectively instructing or configuring the processor or computer
to operate as a machine or special-purpose computer to perform the
operations performed by the hardware components and the methods as
described above. In one example, the instructions or software
include machine code that is directly executed by the processor or
computer, such as machine code produced by a compiler. In another
example, the instructions or software include higher-level code
that is executed by the processor or computer using an interpreter.
Programmers of ordinary skill in the art can readily write the
instructions or software based on the block diagrams and the flow
charts illustrated in the drawings and the corresponding
descriptions in the specification, which disclose algorithms for
performing the operations performed by the hardware components and
the methods as described above.
The instructions or software to control a processor or computer to
implement the hardware components and perform the methods as
described above, and any associated data, data files, and data
structures, are recorded, stored, or fixed in or on one or more
non-transitory computer-readable storage media. Examples of a
non-transitory computer-readable storage medium include read-only
memory (ROM), random-access memory (RAM), flash memory, CD-ROMs,
CD-Rs, CD+Rs, CD-RWs, CD+RWs, DVD-ROMs, DVD-Rs, DVD+Rs, DVD-RWs,
DVD+RWs, DVD-RAMs, BD-ROMs, BD-Rs, BD-R LTHs, BD-REs, magnetic
tapes, floppy disks, magneto-optical data storage devices, optical
data storage devices, hard disks, solid-state disks, and any device
known to one of ordinary skill in the art that is capable of
storing the instructions or software and any associated data, data
files, and data structures in a non-transitory manner and providing
the instructions or software and any associated data, data files,
and data structures to a processor or computer so that the
processor or computer can execute the instructions. In one example,
the instructions or software and any associated data, data files,
and data structures are distributed over network-coupled computer
systems so that the instructions and software and any associated
data, data files, and data structures are stored, accessed, and
executed in a distributed fashion by the processor or computer.
While this disclosure includes specific examples, it will be
apparent to one of ordinary skill in the art that various changes
in form and details may be made in these examples without departing
from the spirit and scope of the claims and their equivalents. The
examples described herein are to be considered in a descriptive
sense only, and not for purposes of limitation. Descriptions of
features or aspects in each example are to be considered as being
applicable to similar features or aspects in other examples.
Suitable results may be achieved if the described techniques are
performed in a different order, and/or if components in a described
system, architecture, device, or circuit are combined in a
different manner, and/or replaced or supplemented by other
components or their equivalents. Therefore, the scope of the
disclosure is defined not by the detailed description, but by the
claims and their equivalents, and all variations within the scope
of the claims and their equivalents are to be construed as being
included in the disclosure.
* * * * *